Drought-stress memory confers cold hardiness in grapefruit (Citrus paradisi) through modulations in antioxidant system, osmolyte production and carbohydrate metabolism

Abstract

Priming is a phenomenon in which plants are initially exposed to mild stress to develop resilience to subsequent or severe stress. There is a lack of scientific knowledge regarding the drought-priming (DP) effect on the freeze tolerance mechanism in cold-sensitive grapefruit (Citrus paradisi). Therefore, the present study was conducted to gain insight into how plants perform under freezing stress (FS) when given short-term drought stress (DS) as a priming event. This study investigated the potential of DP to enhance freeze tolerance in cold-sensitive grapefruit. The plants were subjected to drought-priming at 50 % and 75 % field capacity (FC), with control (non-stress- 100 % FC) for three weeks before being subjected to freezing stress (-6 °C). DP exhibited enhanced freezing tolerance through an improved antioxidant system, osmolyte production, and carbohydrate metabolism. It also triggered the activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione peroxidase (GPX), and ascorbate peroxidase (APX), mitigating oxidative damage caused by reactive oxygen species (ROS). The accumulation of osmolytes, including proline, glycine betaine (GB) and soluble sugars, was also induced, stabilizing cellular structures and maintaining osmotic balance. Additionally, carbohydrate metabolism shifted towards sugar biosynthesis, with reduced starch reserves providing energy for stress adaptation. It is concluded that drought-stress memory as a primer acclimated the plants to freezing stress by alleviating oxidative damage to membranes and maintained high energy production through enhanced antioxidant activities, osmolyte accumulation, and regulating carbohydrate metabolism. This study highlights the practical potential of drought-priming as a cost-effective and non-invasive strategy to improve cold hardiness in citrus and related species. By integrating drought-priming into management practices, growers can enhance the resilience of young grapefruit plants to freezing conditions, contributing to sustainable citrus production in regions prone to cold stress or unexpected freeze events in winter or late summer.